This invention relates to a method and an apparatus for measuring temperatures of hot material including a heated steel plate in an industrial furnace such as a continuous annealing furnace.
Radiation pyrometers or theremometers have been heretofore employed for measuring the temperature of hot material which is heated in an industrial furnace of the above-mentioned type. However, the radiation pyrometer is not necessarily suited for the accurate measurement of temperature of a heated material in the furnace since the pyrometer is influenced by energy radiated from wall surfaces of the furnace. Accordingly, in actual operations, for example, in a steel plate annealing operation in a steel plant, which requires an accurate control of temperature of the heated material, various problems arise due to an inaccurate temperature measurement, adversely affecting the quality of the heated material and the controls of the subsequent treating steps.
Moreover, contact-type thermometers have been used for more accurate measurement of temperatures of heated material by direct contact with the material. However, the direct contact-type thermometer has a disadvantage in that, where a heated material is moved as in a continuous annealing furnace, the surface of the heated material may be damaged by direct contact with the thermometer, with increased abrasive wear of the thermometer itself. Thus, it is difficult to employ a contact type thermometer as well.
It is therefore desirable to measure the temperature of heated material in a non-contacting state, and in this sense, the above-mentioned radiation pyrometers or thermometers have thus far been resorted to. Preferably, the radiation thermometer should be located in a position as close to a heated material as possible so as to reduce a measuring error to a minimum. pg,3 In actual operations, however, a heated material such as a steel plate is not necessarily flat and is often in a wavy form. A wavy heated material has possibility of colliding with and breaking down the radiation thermometer. In order to avoid this, it is necessary to keep the heated material spaced from the radiation thermometer. This invariably results in a measuring error due to the radiation energy from wall surfaces of the furnace.